I've patterned quite a few turkey guns and I've never seen a gun throw a pattern much tighter than a paper plate at 20 yards... Hell even at 10 yards I'm getting a pattern the size of softball...


But then again every year I hear story's of people killing turkeys out too 60-70 yards with shell that have 80% #7 hevi shot...

A factory choke will not compete with aftermarket. Pure Gold, Indian Creek are two of the best spent moneys. HS Undertaker is also a great shooting choke for the money in the cheaper feild. As the guys said above Constriction is important in a good pattern....

Ditto what BT said!!

I'm just a beginner at turkey hunting, other than the factory chokethat comes with the870 turkey gun (which I plan on buying soon) what would be a good aftermarket choke for $40 or less, or should I just use the factory choke? What's everyones opinion on the Jellyhead choke?

The Jellyhead isa pretty good choke, you should be able to get pretty good patterns with it.
Another option might be to contact Pure Gold and see about their reconditioned chokes.